1. Field of the Invention
The present invention relates to a polyester composition principally comprising a polyester and a block copolymer having terminal hydroxyl groups. The polyester composition is excellent not only in heat resistance, solvent resistance and processability, but also in impact resistance.
2. Description of the Related Art
In recent years, polyesters have been, utilizing their excellent heat resistance, solvent resistance, processability and like properties, widely used in the fields of electric parts, electronic parts, automobile parts, industrial machine parts and the like. However, polyesters have insufficient impact strength and relatively high specific gravity among general-purpose engineering plastics, and it has been desired to improve these drawbacks.
To improve the shock resistance of polyesters, incorporation of rubber components into polyesters has been attempted (see, for example Japanese Patent Publication Nos. 5224/1971, 5225/1971, 5227/1971 and 32886/1971). To decrease the specific gravity of polyesters, attempts have been made to blend polymers having low specific gravity such as polyethylene and polypropylene (see, for example, Japanese Patent Application Laid-open No. 147/1978).
With compositions obtained by blending different polymers, there are, in general, very few combinations of compatible components. Thus, when compositions are obtained by blending polyesters with a rubber component, or polyethylene, polypropylene or like polymers, there occur in most cases the problems of non-uniformity, inter-phase delamination and the like due to poor compatibility so that the object of improving the shock resistance or decreasing the specific gravity of polyesters has not been achieved.
There has been reported that a composition comprising a polyester and a block copolymer having a structure of P--Q--P (P: polymer block comprising an aromatic vinyl compound, Q: polymer block comprising a conjugated diene) in which at least 70% of the conjugated diene part is hydrogenated (see, for example, BP 1,581,167 and Japanese Patent Application Laid-open No. 150464/1977). This composition is, however, unsatisfactory in shock resistance and not completely sufficient in tensile elongation.